Data storage devices, such as disc drives, generally utilize slider heads each of which carries a transducer for reading and writing data to storage media, such as discs, housed in the devices. In the case of disc drives, the slider heads hover over the discs at a fly height as the disc is rotated underneath. With continual increases being made in the recording density of storage media, there has been corresponding demand for fly height of the slider heads to be reduced, which would enable more data to be recorded to and read from the heads. However, because of media surface irregularities and operational conditions, decreased fly heights can lead to detrimental contact between transducer and media. Consequently, clearance measurement has become critical for both component and drive clearance setting. For example, microactuators (such as writer heaters) positioned in the slider head have become an important tool in actively controlling clearance between transducer and media, known as head to media spacing (HMS).
Generally, in activating a writer heater, a protrusion thereof is drawn close toward the media surface until contact is made. Following such contact, the HMS can be varied by correspondingly varying the power to the heater. Ideally, one is looking to provide just enough power to the heater so that the protrusion barely contacts the media surface. In turn, friction between the head and media can be minimized so as to not adversely affect future functioning of the transducer. However, if too much power is used, greater friction between the head and media results, which can lead to signal errors during future reading/recording of the transducer.
Thus, a primary concern for active clearance control is reliable and wear-free contact detection. To date, two types of contact detection schemes used in data storage device calibrations have involved (i) detecting off-track signal by measuring change in position error signal (dPES), which results from friction between the head and the contacted media and (ii) detecting modulation from the head-to-media contact.
However, these schemes for detecting contact stand to be improved.